金沙所有登入网址:Two-faced approach creates solar cells to dye for

时间：2017-09-26 04:00:24166网络整理admin

By Colin Barras Solar cells could become cheaper and more efficient, thanks to a cheap dye-based design that can capture sunlight from both sides simultaneously. Dye-sensitised solar cells contain no silicon, but instead rely on the interaction between light and a dye coated on to tiny grains of titanium dioxide, a cheap white pigment. The grains sit in a liquid that acts as an electrolyte, picking up electrons released by the dye as it absorbs light, generating current. The whole mixture is sandwiched between two electrodes; a transparent glass sheet doped with tin oxide to make it conducting and an opaque rear panel. This allows a current to flow when the cell is placed in sunlight But the efficiency of dye-sensitised solar cells designed for outdoor conditions is currently about 金沙所有登入网址. That’s light years from the 42.8% efficiency reached by some silicon solar cells and well below the 15% standard for many silicon designs. Michael Grätzel of the Swiss Federal Institute of Technology in Lausanne, Switzerland – who co-invented dye sensitised solar cells in 1991 – had thought it may be possible to double the efficiency of his low-cost cells simply by designing one that collects light from both sides simultaneously. Now Grätzel’s team, working with Seigo Ito of the University of Hyogo, Japan, has done just that. Their new dye-sensitised solar cell is almost as efficient at converting light into energy when it strikes the rear side as when it strikes the front. To achieve the trick, Grätzel’s team first replaced the opaque back panel with a second sheet of glass, making the entire device transparent. The new panel is also coated with tin oxide and acts as the second electrode, donating electrons back to the electrolyte to complete the circuit. But because it is transparent, it lets light into the system from the rear. Grätzel’s team experimented with varying the thickness of the dye-filled layer. They found that if that layer was around 15 micrometers thick, the solar cell converted 金沙所有登入网址 of the light arriving through its front into electricity and a further 5.5% of the light arriving through the rear. “There is always an albedo effect [as light bounces off surfaces] and on a cloudy day, collecting light from both sides will buy you almost double the normal efficiency,” says Grätzel. Earlier in the summer, another research team that Grätzel works with identified an electrolyte that increased dye-sensitised solar cell efficiency to 8.2% (Nature Materials, DOI: doi:10.1038/nmat2224). “Other electrolytes have reached 10% or even higher,” he says. Using those electrolytes in the new two-sided solar cell could help to reach efficiencies of 15 to 20%, which is better than the performance of silicon wafer solar cells under similar conditions, says Grätzel. Even before Grätzel’s team announced their new cell design, dye-sensitised solar cells were beginning to attract interest from industry. Earlier this year Sony announced it had developed cells with an energy conversion efficiency of 10%, a level considered necessary for commercial use. But those efficiency ratings are misleading according to Robert Hertzberg, chairman and co-founder of G24 Innovations, a company based in Cardiff in the UK that manufactures dye-sensitised solar products. “This technology allows you to capture power in low light, even rainy conditions,” he says. “Silicon cells only allow you to capture power during a short window [when light is intense].” That means the cells give a better performance over the whole day even if they are less efficient under ideal conditions. Journal reference: Nature Photonics (DOI: doi: